1. Technical Field
The present invention relates to a bicycle derailleur and more particularly to a clutch unit capable of enhancing the precision of operation of a bicycle derailleur.
2. Description of Related Art
The conventional bicycle derailleurs, as the one disclosed in U.S. Pat. No. 8,852,041(B2), are composed essentially of a base member, a movable member, and a chain guide. The base member is configured to be fixed to the frame of a bicycle. The movable member is connected to the base member and is configured to rotate the chain guide with respect to the base member about a rotational axis perpendicular to the moving direction of the bicycle, in order for the chain guide to guide the chain of the bicycle to sprockets of different number of teeth, thereby effecting a change in speed and also providing the chain with proper tension to ensure smooth operation.
To tension the chain properly and to reduce unnecessary swinging of the chain guide due to poor road conditions, the bicycle derailleur of the '041(B2) patent is provided with a resistance-applying element that keeps the chain from irregular operation and falling off. The resistance-applying element is provided therein with a one-way clutch that allows rotation in only one direction so as to control the position to which the chain guide is rotated. In the '041(B2) patent, the one-way clutch 178 is a roller clutch, whose precision of operation depends on the number of the roller retainer 234. As the number of the roller retainer 234 is limited by the size of the rollers 230, the operation of the roller clutch cannot be further enhanced in precision, which leaves something to be desired.